ME204: Heat Transfer

Unit 3: Convection
*In this unit, we will study the second mode of heat transfer:
convection. While conduction is the major mode of heat transfer in
solids (as you learned in Unit 2), convection is the major mode of heat
transfer in fluids. Convection occurs because of movements of fluids.
Heat is carried away and dispersed thorough the fluid. Convective heat
transfer occurs in nature (e.g. cooling down effects of wind) and in
engineering systems (e.g. heating of homes, cooling of equipment).

We will examine two major types of convective heat transfer: forced
convection and natural convection. In forced convection, movement of
fluid is due to external forces such as a pump, while in natural
convection, it is due to density differences driven by non-uniformity of
temperature. *

Unit 3 Time Advisory
This unit will take you approximately 32 hours to complete.

☐ Subunit 3.1: 3 hours

☐ Subunit 3.2: 3 hours

☐ Subunit 3.3: 4 hours

☐ Reading: 3 hours

☐ Assignment: 1 hour

☐ Subunit 3.4: 2 hours

☐ Subunit 3.5: 2 hours

☐ Subunit 3.6: 2 hours

☐ Subunit 3.7: 8 hours

☐ Video Lectures: 4 hours

☐ Reading: 4 hours

☐ Subunit 3.8: 8 hours

☐ Video Lectures: 4 hours

☐ Reading: 4 hours

☐ Subunit 3.9: 8 hours

☐ Video Lectures: 4 hours

☐ Reading: 4 hours

Unit3 Learning Outcomes
Upon successful completion of this unit, the student will be able to:

Instructions: Please watch these two science demonstration video,
in which Dr. Julius Summer Miller performed several simple
experiments to illustrate heat convection. You may want to repeat
some of these experiments at home.

Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.

Instructions: Please click on the link “Download A Heat Transfer
Textbook,” which will take you to a download request form. After
you fill in relevant information about you, you will be able to
download the book. Note that the only information required on the
form is your city, country, and occupation. The book is in PDF
format (17.2 MB). Save a copy of the book for future use in this
course. This is one of the best books on heat transfer. Please
read section 6.1 in “Chapter 6: Laminar and Turbulent Boundary
Layers” (pp 271-278). Note that the reading will cover the material
that you need to know for subunits 3.1 and 3.2.

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3.1 Introduction to Boundary LayersNote: This topic is covered by the reading below the Unit 3
introduction.

3.2 Local/Average Convection Coefficients for Heat and Mass TransferNote: This topic is covered by the reading below the Unit 3
introduction.

Instructions: For this unit, please read sections 6.2-6.8 in
“Chapter 6: Laminar and Turbulent Boundary Layers (pp 278-323).”
Note that the reading will cover the material that you need to know
for subunits 3.3-3.6, and any inclusive sub-subunits. In Section
6.2, you may want to skim through page 288 and focus on equation
6.24 on page 289. Make sure that you understand figure 6.11. Pay
attention to sections 6.4 and 6.6, which provide detailed
discussions on the Prandtl number, boundary layer thicknesses, and
the Reynolds analogy. Browse through section 6.5, because we are
going to revisit this section in subunit 3.7.
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displayed on the webpage above.

Link: MIT: Professors John Lienhard IV and John Lienhard V’s A Heat
Transfer Textbook: “[Chapter
7](http://web.mit.edu/lienhard/www/ahtt.html)” (PDF)
Instructions: Please click on the link “Download A Heat Transfer
Textbook,” which will take you to a download request form. After
you fill in relevant information about you, you will be able to
download the book. Note that the only information required on the
form is your city, country, and occupation. The book is in PDF
format (17.2 MB). Save a copy of the book for future use in this
course. This is one of the best books on heat transfer. For this
unit, please read “Chapter 7: Forced Convections in a Variety of
Configurations” (pp. 342-388). Note that the reading will cover the
material that you need to know for subunits 3.7 and 3.8. This
reading will introduce you to heat transfer for external flows, such
as flows over a cylinder, a sphere, and across tube fields and
forced convection heat transfer.
Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.

Instructions: Please watch these videos (ranging from approximately
45-50 minutes for each video), which will introduce you to the basic
concepts of forced convection. These videos cover the material that
you need to know for subunits 3.7 and 3.8. In Lecture 18, pay
attention to definitions of local heat transfer coefficient and
average heat transfer coefficient. Also, make sure that you
remember the definitions of Nusselt number, Reynolds number, and
Prandtl number. In Lecture 19, Professor U.N. Gaitonde works
through an example of convective heat transfer with constant heat
flux at wall.

Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.

3.7.1 Introduction to External FlowNote: This topic is covered by the resources below subunit 3.7.

MIT: Professors John Lienhard IV and John Lienhard V’s A Heat
Transfer Textbook: “[Chapter
6](http://web.mit.edu/lienhard/www/ahtt.html)” (PDF)
Instructions: Please click on the link “Download A Heat Transfer
Textbook,” which will take you to a download request form. After
you fill in relevant information about you, you will be able to
download the book. Note that the only information required on the
form is your city, country, and occupation. The book is in PDF
format (17.2 MB). Save a copy of the book for future use in this
course. This is one of the best books on heat transfer. For this
sub-subunit, please read sections 6.5 in “Chapter 6: Laminar and
Turbulent Boundary Layers” (pp. 278-323) carefully. The reading
introduces you to equations that can be used to calculated heat
transfer coefficient of forced convection over a flat plate.
Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.

3.7.3 Flow across a CylinderNote: This topic is covered by the resources below subunit 3.7

3.7.4 Flow over a SphereNote: This topic is covered by the resources below subunit 3.7

3.7.5 Flow across Tube FieldsNote: This topic is covered by the resources below subunit 3.7

Instructions: Please click on the above link, which will take you
to a webpage of heat transfer experiments captured by Infrared
video. Browse to the sections titled “Natural Convection - A
Vertical View” and “Natural Convection - A Horizontal View.” Read
the descriptions and watch the videos. Click on the link “Read
more” if you are interested in a more detailed description of the
experiments. The videos will provide you some insights into the
dynamics of natural convection.

Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.

Instructions: For this subunit, please read sections 8.1-8.4 (pages
399-416), which will introduce you to natural convection and
dimensionless numbers characterizing natural convective heat
transfer. Make sure that you know how to define the Raleigh number
for different geometrical configuration of the heating surface
(section 8.3).

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Instructions: Open the link above that will take you to the
homepage of ME 375 – Heat Transfer taught by Professor Larry
Caretto. Click on "April 11": to download the Word file hw09.doc.
Solve all the problems listed in the homework. For each problem,
read the problem statement in bold and attempt to solve it. After
you complete your solutions, check with the answers below each
problem statement.
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